1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for establishing a call connection within a cellular network, and specifically to reducing the call setup time for calls within an internet protocol based cellular network.
2. Background of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a sample GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC 14 provides a circuit-switched connection of speech and signaling information between a Mobile Station (MS) 20 and the PLMN 10. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which the MS 20 may move freely without having to send update location information to the MSC 14 that controls the LA 18. Each LA 18 is divided into a number of cells 22. The MS 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS 24 is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS""s 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that PLMN 10. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
As the amount of traffic within cellular networks 10 increases, so does the amount of time required to setup a call to or from an MS 20. Long call setup times are frustrating to calling subscribers. The longer the call setup time, the less likely the calling subscriber will be to use the system, and the lower the perceived quality of the system. Currently, little is being done to shorten the call setup time. In some cases, an attempt is made to mollify the calling subscriber by playing tones or announcements while they are waiting for the connection to go through. These tones or announcements really only tell the calling subscriber that something is happening, but it does not speed up the connection time.
The present invention is directed to telecommunications systems and methods for decreasing the average call setup time in a cellular network. Existing call setup procedures are based on establishing a circuit connection. At the end of the call, the circuit connection is released. In order to setup another call, another circuit connection must be established. However, in Internet Protocol (IP)-based cellular networks, circuits are not used. Instead, the bandwidth is shared as an aggregate. Therefore, by using an IP-based cellular network, call information (such as routing information, channel types, etc.) for a particular call initiated by a calling MS can be stored in a call cache within a serving Mobile Switching Center (MSC) to immediately allow a call to the same called party number with the same bearer capabilities set to be re-established without tying-up circuits. A call cache identifier (CCI) can be assigned to that call cache. This CCI is preferably stored in both the MSC and in the calling MS. When the calling MS wants to re-establish a previous call, the calling MS can include the CCI for that previous call with the call setup message. Thereafter, the MSC accesses the call cache associated with the received CCI, and uses the call setup information stored in the call cache to re-establish the call.